A Parametric And Stability Analysis Of Liquid Between Rolls In Reverse Coating Under Different Speed Ratio

The law of the liquid distribution between two rolls in reverse roll coating has been studied. The flow of liquid between the applicator and the pick-up roll has been streamline into the viscous flow between two infinite flat. Then the hydrodynamic lubrication theory and the capillarity condition have been combined to establish a mathematical model of the roll coating, from which one-dimension Reynolds equation is derived. And then the equation has been solved and the stability of the process of the reverse coating has been investigated too.Then the influence of changing roll coating parameters (the roll speed ratio, the roll radius, the surface tension of liquid coating ,the entrance oil film thickness and the gap thickness between the two rolls)on the pressure distribution of the meniscus area and the fluid between the rolls have been emphatically analyzed under different circumstances. The main conclusions are obtained as follows.(1) When the applicator roll is rigid, the applicator roll film thickness varies with the changing of the process parameters, which is always larger than the entrance oil film thickness.(2) The impact of roll speed ratio is an important factor in coating thickness. In any case, the applicator roll film thickness always increases with the speed ratio.(3) The stable and uniform film of applicator roll can be more easily got while the applicator roll is covered with a rubber layer without gap between rolls.(4) When the applicator roll is rigid, the pressure between rolls increases with the roll radius; when the applicator roll is an elastomeric roll, the pressure decreases with the roll radius.Such evaluations are used to enhance the usefulness of the roll coating and develop design guidelines.